1. Field of the Invention
The present invention relates to injectors and nozzles, and more particularly to injectors and nozzles for atomizing liquids.
2. Description of Related Art
The drive for cleaner, quieter, and more efficient aircraft has created a demand to develop lean burn jet engines, where most of the combustion air enters the combustor via the fuel injectors. Lean burning combustion creates leaner, lower temperature flames, which reduces the NOx emissions and improves fuel efficiency. However, maintaining stability over the entire power curve can be a challenge in lean burning engines, especially at low power conditions. The fuel injection process becomes extremely critical at low power conditions, where fuel and air must be mixed very rapidly to achieve flow patterns that yield a stable flame.
Numerous fuel injection methods have been examined with an aim to advancing the art of lean burn technologies. Two such fuel injection methods include Lean Direct Injection and Lean Premixed Pre-vaporized Injection. Lean Direct Injection (LDI) introduces liquid fuel directly into the flame zone as opposed to Lean Premixed Pre-vaporized Injection (LPP), where fuel is mixed with air and vaporized upstream of the flame zone. While LPP provides excellent mixing, its implementation is complicated by auto-ignition and flashback into the premixing region. These complications have steered increasing interest toward LDI as a superior injection method because it avoids premature ignition by mixing air and liquid droplets directly in the combustion zone.
In researching LDI technologies, NASA has conducted in-depth research on a number of multipoint LDI fuel injectors including injectors having nine, twenty-five, thirty-six, and forty-nine individual injection points in a flame tube combustor and a sector rig. All of these configurations have demonstrated the ability of multipoint injection to dramatically reduce NOx emissions. A similar multipoint injector having a square, thirty-six injection point array is described in U.S. Pat. No. 6,533,954 to Mansour et al.
The multipoint injectors that have been investigated by NASA and others have generally employed flat, rectangular arrays of injection points. Swirling air is introduced around each injection point, producing small, individual recirculation zones for flame anchoring. Although tests of these multipoint injectors have shown some promise in reducing emissions, there is still a need to improve the stability. Moreover, most medium and large gas turbine engines in use employ air blast injectors. In these designs, fuel is deployed as a conical sheet and is broken up into droplets as it is sheared by inlet air that is accelerated by concentric swirlers. A central recirculation zone created by the large air swirlers serves to anchor the flame and provide stability. The multipoint injectors of NASA and others described above are not conducive to operating in the same physical envelope as traditional air blast injectors, especially with respect to providing the volume of airflow and dominant aerodynamic structure for flame anchoring, typical of air blast injectors.
Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for LDI multipoint injectors that allow for improved flame stabilization. There also remains a need in the art for such injectors that can be used in traditional injector envelopes within gas turbine engines. The present invention provides a solution for these problems.